Using Dometic refrigerator on 12 volts

[Raz]

Originally Posted by GaryM

..... I traded for a 2015 Ford Explorer which had a factory tow package with a 7-pin connector, but only used 14 gauge wire to supply current to the camper battery. After towing the camper for 4-5 hours with the fridge running on 12 volts, the battery in the camper would no longer run the fridge. The culprit was the 14 gauge wire, not the alternator.

The use of 14 gauge wire may have been intentional. I have to assume the engineers that designed the tow package wiring knew the application.

Consider, the voltage drop across the charge line is the difference between the two batteries. This makes the charge line current that voltage divided by the charge line resistance or:

I charge = (Vtow-Vtrailer)/Rchargeline

Basically the charging current is a function of Vtow (alternator output) and the charge line resistance (determined by the wire gauge). By using a small wire they limit the load on the alternator for that application. The smaller wire will still let the battery charge ( it just takes a little longer) but limits additional loads (like the fridge). And the use of a smaller alternator reduces the cost to manufacture the vehicle which makes the bean counters happy.

[Borrego Dave]

I think you've hit the nail on the head Raz and basically what I've been thinking also. The tow "package" was designed for charging the TT battery/s while towing and not for running a 12V refer as the vast majority of RV owners wouldn't even give that a second thought. It can and is done by a few folks but most of them are using a dedicated 12V only trucker type fridges and not the standard RV 3 way units.

[Darral T.]

That appears to be the "Argosy" by Airstream...not an egg.

Originally Posted by Raz

And it's an egg. .

RV Propane System Safety Tips And Precautions

[Darral T.]

You guys can surmise all you want. I ran a 10ga wire WITH a breaker installed and have NO problems running the 3-way fridge. I guess the "engineers" didnt know what they were doing at Dometic? It appears on this forum that the guys that cant run their fridge on 12v declares it's impossible for those of us who do.

They also told the Wright Brothers their plane would never get off the ground. If it DID it wouldnt stay up. If it STAYED up it would crash.... on and on we go. They flew it anyway. I think yall get the point.

Originally Posted by Borrego Dave

I think you've hit the nail on the head Raz and basically what I've been thinking also. The tow "package" was designed for charging the TT battery/s while towing and not for running a 12V refer as the vast majority of RV owners wouldn't even give that a second thought. It can and is done by a few folks but most of them are using a dedicated 12V only trucker type fridges and not the standard RV 3 way units.

[WizWid]

Originally Posted by Darral T.

You guys can surmise all you want. I ran a 10ga wire WITH a breaker installed and have NO problems running the 3-way fridge. I guess the "engineers" didnt know what they were doing at Dometic? It appears on this forum that the guys that cant run their fridge on 12v declares it's impossible for those of us who do.

They also told the Wright Brothers their plane would never get off the ground. If it DID it wouldnt stay up. If it STAYED up it would crash.... on and on we go. They flew it anyway. I think yall get the point.

Hey Darral,

Just curious as I only run on propane on the road, but do you know if your tow vehicle is supplying enough juice to really run the fridge for a long time? In other words at the end of a long trip is the battery as fully charged as it was at the start?

Jim

[Raz]

Originally Posted by Darral T.

That appears to be the "Argosy" by Airstream...not an egg.

While I'm sorry to see it happen I was afraid it was someone's Boler just finished from an off frame restore.

[EarlFurman]

"How long can I run my Dometic fridge on 12 volts when traveling in my recently acquired 1997 Scamp 13? .... The Dometic manual says it draws 10.5 amps and is rated at 25 watts."

We had a 3-way that was rated at 19 amps on DC. Using it on 12v was, as you can imagine, not ideal except for a very short time. Skipping all the intermediate steps, what we finally ended up with was: (1) 6 gauge wire, with 30 amp breaker, from battery to Anderson plug on rear of TV. (2) 6 gauge wire from Anderson plug on bar at front of trailer to a CTEC D250S (also used for our solar) that charged the trailer battery. (3) a low voltage cut out (can't remember which) between the trailer battery and the 'fridge (so as not to drain the trailer battery during stops).

For most people this extra work may not be worth it just to run the 'fridge on 12v while driving.

Suggestion: First I doubt that your four pin plug supplies 12v to your trailer battery. How does the trailer battery get charged? Second consider running thick enough wire from your TV to your trailer and on to the 'fridge. then measure the voltage at the 'fridge while operating on 12v. Only if the voltage is too low go on to the more extreme setup we used.

[Darral T.]

As I posted earlier, I've ran this setup for the past 8 yrs (in April) and NEVER had a dead battery. We're talking on the road ALL day- up to 8 hours running and even stopped for breakfast leaving the fridge on AND connected to my truck. Never a problem. If some dont believe that, I'm sorry, but it works for me and I have a 4 cyl Nissan with NO tow package. I installed it (7-pin plug) myself as I mentioned running all the wiring including the 10ga wire. I also installed the Prodigy brake controller myself as well. No over-sized alternator, no HD battery...all stock.

Here's the "kit" I ordered from etrailer.com. I also ordered extra wire- good thing, and the brake controller! https://www.etrailer.com/Accessories...ler/ETBC7.html

The Group 27-sized battery in my trailer is ALSO 8 yrs old. But I keep a "Battery Tender JR" on it 24/7.

BTW, I see you're formally from Orbital Machine Works. I'm a machinist/draftsman by trade. I'm IT now but still own a lathe/mill combo with lotsa tooling (the most expensive of machine tools!).

Originally Posted by widgetwizard

Hey Darral,

Just curious as I only run on propane on the road, but do you know if your tow vehicle is supplying enough juice to really run the fridge for a long time? In other words at the end of a long trip is the battery as fully charged as it was at the start?

Jim

[Raz]

Darral, what year is your truck.

[Darral T.]

'99 Frontier - 5 spd Manual.

A pic of my setup when I was bringing it home from Backus in 2010.

https://www.flickr.com/photos/50351683@N08/5926020415/

Originally Posted by Raz

Darral, what year is your truck.

[Raz]

Nice job. I could run the fridge with my '03 Tundra . My Nissan has a much larger electrical demand. Truthfully I've never bothered trying. On the road I run the propane at night which keeps the salad stuff fresh. We always have an ice chest for milk etc. and typically shop for dinner daily. When camped in one place I use the propane.

[TomK]

Originally Posted by Darral T.

'99 Frontier - 5 spd Manual.

A pic of my setup when I was bringing it home from Backus in 2010.

https://www.flickr.com/photos/50351683@N08/5926020415/

I believe you Darral. I've seen your work

Tom

[Borrego Dave]

Originally Posted by Darral T.

You guys can surmise all you want. I ran a 10ga wire WITH a breaker installed and have NO problems running the 3-way fridge. I guess the "engineers" didnt know what they were doing at Dometic? It appears on this forum that the guys that cant run their fridge on 12v declares it's impossible for those of us who do.

Darral, we're talking two different things here it seems. No one has said anything against Domectic engineering, they do work on 12V. Newbies to the forum or RVing ask why they have a dead battery after trying it. The answer, with no surmising, is the tugs FACTORY designed towing package with a light duty charging wire that was never meant to operate a refer on the road. You and others have rewired your tugs to over come that, great. Not everyone has the interest or need to run 12V but I'm certainly not going to knock you of your 12V choice.

[Raspy]

Originally Posted by Darral T.

You guys can surmise all you want. I ran a 10ga wire WITH a breaker installed and have NO problems running the 3-way fridge. I guess the "engineers" didnt know what they were doing at Dometic? It appears on this forum that the guys that cant run their fridge on 12v declares it's impossible for those of us who do.

I did the same thing on an earlier camper I had, no problem. My Dometic will run just fine on 12 volts, with my Ram 7 pin wiring, and it also did with the previous owner and their F-150.

The wire size only tells you how many amps the manufacturer is willing to send to the trailer, it doesn't tell you the limits of the alternator. The wire size is not the limit, the manufacturer designed amp limit determines the wire size. The limit is determined by the computer or the circuitry, not the wire. Truck alternators are typically about 60 amp minimum and about 130 amps maximum. They will produce plenty of power, even at idle, for a fridge that only needs about 11 amps.

What I did on an earlier camper, with an earlier truck, as Darral described, was to run #10 conductors (+ and -) directly from the battery, with a 30 amp circuit breaker in-line.

The only possible problem with this is that the load continues after the engine is shut off, so you can run the truck battery down after enough time. If the batteries are fully charged, a few hours of running the fridge will not be a problem as far as running the truck battery down.

If your camper battery will not achieve full charge will running the fridge, it might be a good idea to run a new charging wire directly from the TV battery.

[Chris from Comox]

I concur with Ziggy and turn off the propane when I tow in both Canada and the USofA for the simple reason that when one pulls into a gas station to refuel , I don’t think it’s a good idea to bring an open flame to the same place other folks are known to spill gas nearby..

[Jann Todd]

Originally Posted by Jim er

The heating elements for a Dometic frig when running, measure at about 150W. At 110V it only takes ~1.4A to run the frig when it needs cooling. At 12V, it takes about 12.5A and the reason any battery is quickly discharged at that huge a drain rate. If your frig is already at temp, then it will only demand 12V when it gets above a set temp and turns off when it reaches the set lower temp. On a warm day, you can expect 12V demand to be 90% on or more. If running solar, then usually the solar will catch the battery back up during the off periods.

I personally run on propane while traveling. My later model Dometic frig switches automatically to 110 when plugged in and back to propane when not plugged in.

I do believe the people who say there is a fire risk when using propane while traveling. The odds of it happening as far as I am concerned, are slim and none. Not having to worry about food spoilage and ice cream melting, priceless.

Consider the gas station warning signs: no smoking and turn your engine off. Then a car rolls in besides you and guess what, his engine is running and he could be smoking with a window open. How many times has that caused a fire?

I worry about the big stuff, not about running my frig on propane.

I agree with you totally on running the fridge on propane while traveling. We have for over 40 years. Our policy for fueling is to stop at the entrance of the station and turn off the fridge then fuel and go away from the pumps and turn it on. Only takes about a total of 2-3 minutes for both. We have good hard ice cream and cold food that won't spoil this way. Just because food feels cold doesn't mean it is at a safe temperature to eat.

[Jann Todd]

Originally Posted by nigeleccleston

Thank you! Yes I do have a three-way. I read a few posts from people who keep their fridge cold using propane while driving, I'll go back and see what the downside of that might be. I can always just bring along a cooler and transfer things to that while I'm driving.

If you let your fridge get warm while traveling remember it will take several hours to chill it down again. Propane tanks don't explode. They will vent when they get overheated. We had a friend that had an RV fire caused by badly repaired wiring in a motorhome. As it burned the propane tank would shoot a huge flame across the road when the pressure built up in the tank then quit until the pressure built up again from the heat of the fire. The tank did not explode. I googled propane tanks exploding and they don't, they vent. I'm sure there are exceptions to this just like everything else. We had a friend that rolled a Casita and no problem from the propane tanks either. He was hit by an out of control driver coming the other way and she hit the trailer rolling it. If your tanks are attached like they should be good and tight the likelihood of them coming off is slim. The professionals of propane use and RV'ing say travel is ok with the tanks on and the fridge running.

[Raz]

Originally Posted by Raspy

The limit is determined by the computer or the circuitry, not the wire.

A wire is a resistor. By definition it limits current.

Truck alternators are typically about 60 amp minimum and about 130 amps maximum. They will produce plenty of power, even at idle, for a fridge that only needs about 11 amps.

This may have been true 20 years ago but with all the additional electrical components on any new vehicle I'm not sure only 11amps is the term I'd use.

If your camper battery will not achieve full charge will running the fridge, it might be a good idea to run a new charging wire directly from the TV battery.

Since the factory charge line is typically included in the tow package why didnt the manufacturer use 10 ga wire to begin with? I doubt it's cost. Also, if you connect directly to the battery on many vehicles, my Nissan included, the computer will not know about the additional load. The current sense is between the battery post and the frame. I wouldn't add anything without knowing what effect it will have on every thing else. I'm a retired E.E. I love to tinker. I never worked in the Auto field but am familiar with what is being done. At least enough to know to be cautious. I'm sorry to say the days of seat of the pants backyard engineering are gone. Like I said, I love to tinker.

[Carl Pa]

I use my 1.9 fridge in my 16' scamp on 12 volt, all the time. I run it at least 24 hours at home b/4 i leave, every thing that goes in the fridge is coming from my home fridge to the scamps fridge with some frozen ice packs or water bottles. I travel anywhere from 2 hours to 6 hours at one time. I do unplug if i stop for more then a half hour, but that is just me. Carl

[Darral T.]

Good points Raz. I agree 100%.

Alot of this topic has brought something to light that I will DEFINITELY consider when I trade vehicles. I've always said that my next TOW will DEFINITELY have the "tow package". But what does that EXACTLY consist of and will it do what I want it to do?? Interesting.

I "dodged a bullet" with my Frontier I admit. Meaning? That the newer vehicles hookups at the tail lights are TOTALLY different now than my older-school Nissan. For instance, I first installed the Flat-4 pin to pull a U-Haul trailer (long before I knew I was getting a Scamp!). I had to have special wiring harness because my signal lights was separate (amber) from the brake lights (2-element tail light bulb). This special harness was called the "Tail light converter" but was a breeze to install. Then when I installed the 7-pin, fortunately, the Hopkins setup simply allowed me to plug in my 4-pin and not rerun/rewire the 7-pin entirely. I 'hot-wired' off one of my "backup" lights in the truck...no problem. Of course I ran the brake and "hot" wire to round out the full 7-pin adapter.

NOW, the newer vehicles as I mentioned have low-voltage/amperage setups in the lights. Floyd cautioned me about this years ago. In other words, "hot wiring" to a back light on a new vehicle would cause a possible "overload"! What??? (Maybe LED trailer lights on the RV would make a difference?)

Yep Raz.....the "Shade tree" hook ups, mechanics, etc are falling by the ways side FAST because of the newer "technology" built into vehicles.

Originally Posted by Raz

A wire is a resistor. By definition it limits current.

This may have been true 20 years ago but with all the additional electrical components on any new vehicle I'm not sure only 11amps is the term I'd use.

Since the factory charge line is typically included in the tow package why didnt the manufacturer use 10 ga wire to begin with? I doubt it's cost. Also, if you connect directly to the battery on many vehicles, my Nissan included, the computer will not know about the additional load. The current sense is between the battery post and the frame. I wouldn't add anything without knowing what effect it will have on every thing else. I'm a retired E.E. I love to tinker. I never worked in the Auto field but am familiar with what is being done. At least enough to know to be cautious. I'm sorry to say the days of seat of the pants backyard engineering are gone. Like I said, I love to tinker.